Semiconductor device and method for manufacturing the same

ABSTRACT

Provided is an optical semiconductor device includes: a light-emitting layer having a first main surface, a second main surface opposed to the first main surface, a first electrode and a second electrode which are formed on the second main surface; a fluorescent layer provided on the first main surface; a light-transmissive layer provided on the fluorescent layer and made of a light-transmissive inorganic material; a first metal post provided on the first electrode; a second metal post provided on the second electrode; a sealing layer provided on the second main surface so as to seal in the first and second metal posts with one ends of the respective first and second metal posts exposed; a first metal layer provided on the exposed end of the first metal post; and a second metal layer provided on the exposed end of the second metal post.

CROSS REFERENCE OF THE RELATED APPLICATION

This application is a division of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 14,023,641, filed Sep. 11, 2013,which is a divisional of U.S. Ser. No. 12,556,134, filed Sep. 9, 2009,now U.S. Pat. No. 8,581,291, and claims the benefit of priority fromJapanese Patent Application No. 2008-312453, filed on Dec. 8, 2008; theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical semiconductor device and amethod for manufacturing the same.

2. Description of the Related Art

In response to the development of a high-intensity optical semiconductorelement that emits blue light, there has been commercialized an opticalsemiconductor device that emits white light by using an opticalsemiconductor element that emits blue light and a phosphor capable ofwavelength conversion from blue light into yellow light. Such an opticalsemiconductor device that emits white light has characteristics of:being small in size; emitting high-intensity light relative to asupplied power amount; having a long life; and using no toxic substancesuch as mercury. These characteristics allow the optical semiconductordevice to be increasingly used in various fields such as application toan under-button light source or a flash light source for portable phoneand application to an interior light source and an exterior light sourcefor vehicle.

In terms of total flux relative to a supplied power amount, an opticalsemiconductor device using blue LEDs currently has an efficiency of 150lm/W, which is larger than those of conventional light sources such asan incandescent light bulb (15 lm/W to 20 lm/W) and a fluorescent lamp(60 lm/W to 90 lm/W). However, in terms of cost required for one lm, theoptical semiconductor device has a problem of requiring cost more thanten times higher than the conventional light sources which require 0.1yen/lm to 0.2 yen/lm. As a measure to reduce the cost, there has beenstudied a structure of an optical semiconductor device allowing costreduction while enhancing the luminous efficiency of an element therein.

The most general optical semiconductor device that has beencommercialized has a structure including: an optical semiconductorelement that emits blue light; an Ag-plated Cu frame formed of a whitethermoplastic resin by molding, and used as a wiring board; a connectionmaterial for connecting the optical semiconductor element and the frame;a gold wire through which a current flows between the frame and a topsurface electrode of the optical semiconductor element; and a siliconeresin mixed with phosphor particles for wavelength conversion from bluelight into yellow light and sealing in the optical semiconductor element(see JP-A No. 2000-183407 (KOKAI), for example).

In manufacturing this optical semiconductor device, a whitethermoplastic resin is firstly formed into the Ag-plated Cu frame bymolding. Then, a connection resin is applied onto a portion, on whichthe optical semiconductor element is to be mounted, of the frame.Thereafter, the optical semiconductor element is mounted on the portion,and the connection resin is hardened by heating in an oven. Thereby, theoptical semiconductor element is connected to the frame. Then, by usinga wire bonder, the electrode formed on the chip top surface of theoptical semiconductor element is connected to the frame with an Au wire.Thereafter, a silicone resin with a phosphor concentration adjusted toallow the optical semiconductor device to emit white light is applied,by a dispense technique, around the portion in which the opticalsemiconductor element is mounted, and then hardened by heating. Lastly,a product portion including the optical semiconductor element is cutoff, and the frame used as an exterior electrode is finished by aforming process. Thereby, the optical semiconductor device is completed.

As described above, a conventional optical semiconductor device ismanufactured by incorporating a blue light semiconductor element in astructure of an optical semiconductor device that, in most cases, hasbeen commercialized using an optical semiconductor element that emitslight having a wavelength of 500 nm or more. The optical semiconductordevice that emits such long-wavelength light has a high directivity andhas thus been applied to devices for vehicle, display panels, amusementmachines and the like.

Such a conventional optical semiconductor device manufactured as abovehas a problem of having a shorter life for reasons, such as that bluelight, which has a short wavelength and a high intensity, discolors areflector resin having benzene ring. In addition, an opticalsemiconductor device that emits white light commercialized in responseto the development of a high-intensity optical semiconductor elementthat emits blue light has been increasingly applied to lightingapparatuses as well as conventionally-applied apparatuses such asdevices for vehicle and display panels. With this trend, cost reductionof the optical semiconductor device has been indispensably required.However, the conventional structure of an optical semiconductor deviceonly allows limited cost reduction, and thus the structure and themanufacturing process of the optical semiconductor device has beenrequired to be reconsidered.

In addition, when an optical semiconductor device is applied to alighting apparatus, a light source therein cannot be formed of a singleoptical semiconductor device. Accordingly, in order to replace a generallighting apparatus, such as a fluorescent lamp, with an apparatus usingan optical semiconductor device that emits white light, the apparatusneeds to include multiple optical semiconductor devices. In this case,to eliminate defects such as nonuniform intensity in a light-emittingsurface, a large number of small optical semiconductor devices need tobe mounted on a wiring board. Accordingly, the size reduction of theoptical semiconductor device has also been required.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an opticalsemiconductor device that is capable of suppressing the life reductionthereof, that can be manufactured at reduced cost, and that can beminiaturized approximately to the size of an optical semiconductorelement, and to provide a method for manufacturing such an opticalsemiconductor device.

A first aspect according to an embodiment of the present invention is anoptical semiconductor device includes: a light-emitting layer having afirst main surface, a second main surface opposed to the first mainsurface, a first electrode and a second electrode which are formed onthe second main surface; a fluorescent layer containing phosphorparticles and provided on the first main surface; a light-transmissivelayer provided on the fluorescent layer and made of a light-transmissiveinorganic material; a first metal post provided on the first electrode;a second metal post provided on the second electrode; a sealing layerprovided on the second main surface so as to seal in the first andsecond metal posts with one ends of the respective first and secondmetal posts exposed; a first metal layer provided on the exposed end ofthe first metal post; and a second metal layer provided on the exposedend of the second metal post.

A second aspect according to an embodiment of the present invention is amethod for manufacturing an optical semiconductor device, includes:manufacturing a light-emitting substrate by forming multiple groups ofpositive and negative electrodes on a first main surface of alight-emitting layer, the positive and negative electrodes being used tocause a current for exciting the light-emitting layer to flow throughthe light-emitting layer; manufacturing a fluorescent substrate byforming, on a light-transmissive inorganic film, a fluorescent layermade of a resin in which phosphor particles are dispersed; bonding thefluorescent layer of the fluorescent substrate onto a second mainsurface of the light-emitting layer which is opposed to the first mainsurface; and separating the bonded substrate into pieces each includingone of the groups of the positive and negative electrodes.

A third aspect according to an embodiment of the present invention is amethod for manufacturing an optical semiconductor device, includes:forming multiple light-emitting layers on a substrate, thelight-emitting layers each having a first main surface, a second mainsurface opposed to the first main surface, a first electrode and asecond electrode which are formed on the second main surface; forming aconductive film on the substrate, on which the multiple light-emittinglayers are formed, so that the conductive film covers the multiplelight-emitting layers; forming a sacrifice layer on the conductive film,the sacrifice layer having openings located respectively on the firstand second electrodes of all of the light-emitting layers; formingplated layers respectively on the first and second electrodes of all ofthe light-emitting layers by electroplating using the conductive film asa negative electrode; removing the sacrifice layer and the conductivefilm from the substrate on which the plated layers are formed; forming asealing layer on the substrate from which the sacrifice layer and theconductive film are removed, the sealing layer sealing in the platedlayers of all of the light-emitting layers; exposing one ends of therespective plated layers of all of the light-emitting layers from thesealing layer; forming a fluorescent layer containing phosphor particleson a light-transmissive substrate made of a light-transmissive inorganicmaterial; bonding the fluorescent layer formed on the light-transmissivesubstrate onto all of the light-emitting layers; forming metal layersrespectively on the exposed ends of the plated layers of all of thelight-emitting layers; and separating the resultant substrate intopieces each including one of the light-emitting layers.

A fourth aspect according to an embodiment of the present invention is amethod for manufacturing an optical semiconductor device, includes:forming multiple light-emitting layers on a substrate, thelight-emitting layers each having a first main surface, a second mainsurface opposed to the first main surface, a first electrode and asecond electrode which are formed on the second main surface; forming aconductive film on the substrate, on which the multiple light-emittinglayers are formed, so that the conductive film covers the multiplelight-emitting layers; forming a sacrifice layer on the conductive film,the sacrifice layer having openings located respectively on the firstand second electrodes of all of the light-emitting layers; formingplated layers respectively on the first and second electrodes of all ofthe light-emitting layers by electroplating using the conductive film asa negative electrode; removing the sacrifice layer and the conductivefilm from the substrate on which the plated layers are formed; forming asealing layer on the substrate from which the sacrifice layer and theconductive film are removed, the sealing layer sealing in the platedlayers of all of the light-emitting layers; exposing one ends of therespective plated layers of all of the light-emitting layers from thesealing layer; forming a fluorescent layer containing phosphor particleson all of the light-emitting layers; forming a light-transmissive layermade of a light-transmissive inorganic material on the fluorescentlayer; forming metal layers respectively on the exposed ends of theplated layers of all of the light-emitting layers; and separating theresultant substrate into pieces each including one of the light-emittinglayers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a schematic structure of anoptical semiconductor device according to a first embodiment of thepresent invention.

FIG. 2 is a plan view showing the lower surface of the opticalsemiconductor device shown in FIG. 1.

FIG. 3 is a cross-sectional view showing a schematic structure of anoptical semiconductor device according to a second embodiment of thepresent invention.

FIG. 4 is a cross-sectional view showing a schematic structure of anoptical semiconductor device according to a third embodiment of thepresent invention.

FIG. 5 is a plan view showing the lower surface of the opticalsemiconductor device shown in FIG. 4.

FIG. 6 is a cross-sectional view showing a schematic structure of anoptical semiconductor device according to a fourth embodiment of thepresent invention.

FIG. 7 is a cross-sectional view showing a schematic structure of anoptical semiconductor device according to a fifth embodiment of thepresent invention.

FIG. 8 is a first process cross-sectional view for illustrating amanufacturing method according to a sixth embodiment of the presentinvention.

FIG. 9 is a second process cross-sectional view.

FIG. 10 is a third process cross-sectional view.

FIG. 11 is a fourth process cross-sectional view.

FIG. 12 is a fifth process cross-sectional view.

FIG. 13 is a sixth process cross-sectional view.

FIG. 14 is a seventh process cross-sectional view.

FIG. 15 is an eighth process cross-sectional view.

FIG. 16 is a ninth process cross-sectional view.

FIG. 17 is a tenth process cross-sectional view.

FIG. 18 is an eleventh process cross-sectional view.

FIG. 19 is a twelfth process step cross-sectional view

FIG. 20 is a first process cross-sectional view for illustrating amanufacturing method according to a seventh embodiment of the presentinvention.

FIG. 21 is a second process cross-sectional view.

FIG. 22 is a third process cross-sectional view.

FIG. 23 is a fourth process cross-sectional view.

FIG. 24 is a first process cross-sectional view for illustrating amanufacturing method according to an eighth embodiment of the presentinvention.

FIG. 25 is a second process cross-sectional view.

FIG. 26 is a third process cross-sectional view.

FIG. 27 is a fourth process cross-sectional view.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(First Embodiment)

With reference to FIGS. 1 and 2, a first embodiment of the presentinvention will be described.

As shown in FIG. 1, an optical semiconductor device 1A according to thefirst embodiment of the present invention includes: a light-emittinglayer 2, an adhesive layer 3, a fluorescent layer 4, alight-transmissive layer 5, a reflective layer 6, a first electrode 7 a,multiple second electrodes 7 b, a first metal post 8 a, multiple secondmetal posts 8 b, an insulating layer 9, a sealing layer 10, a firstmetal layer 11 a and multiple second metal layers 11 b. Thelight-emitting layer 2 has a first main surface M1 and a second mainsurface M2. The adhesive layer 3, the fluorescent layer 4 and thelight-transmissive layer 5 are sequentially provided on the first mainsurface M1. The reflective layer 6 is provided on a first region of thesecond main surface M2 of the light-emitting layer 2. The firstelectrode 7 a is provided on a second region of the second main surfaceM2. The second electrodes 7 b are provided on the reflective layer 6.The first metal post 8 a is provided on the first electrode 7 a. Thesecond metal posts 8 b are provided on the respective second electrodes7 b. The insulating layer 9 is provided on regions, other than thosewith the metal posts 8 a and 8 b, of the second main surface M2 of thelight-emitting layer 2. The sealing layer 10 is provided on theinsulating layer 9 so as to seal in the metal posts 8 a and 8 b. Thefirst metal layer 11 a is provided on one end of the first metal post 8a. The second metal layers 11 b are provided on one ends of the secondmetal posts 8 b, respectively.

The light-emitting layer 2 is formed of first and second cladding layers2 a and 2 b, and an active layer 2 c. The first cladding layer 2 a is ann-type semiconductor layer. The second cladding layer 2 b is a p-typesemiconductor layer, and is smaller in area than the first claddinglayer 2 a. The active layer 2 c is held between the first and secondcladding layers 2 a and 2 b. The light-emitting layer 2 has a thicknessof 5 μm, and is formed, for example, of InGaN layers that emit bluelight. Note that the upper surface (in FIG. 1) of the first claddinglayer 2 a serves as the first main surface M1, and the lower surface (inFIG. 1) of the second cladding layer 2 b and part of the lower surface(in FIG. 1) of the first cladding layer 2 a collectively serve as thesecond main surface M2, which has a step.

As shown in FIG. 2, the planar shape of the first cladding layer 2 a isa square 550 μm on a side (see the dotted line of FIG. 2). On a region,not including a corner region (a square 150 μm on a side), of the lowersurface (in FIG. 1) of the first cladding layer 2 a, the second claddinglayer 2 b is formed with the active layer 2 c interposed therebetween.The active layer 2 c has the same shape and approximately the same areaas the second cladding layer 2 b.

The adhesive layer 3 is made of a silicone resin. The adhesive layer 3has a thickness not more than 1 μm, for example, and bonds thefluorescent layer 4 and the first main surface M1 of the first claddinglayer 2 a of the light-emitting layer 2 together. Specifically, as thesilicone resin, methyl phenyl silicone having a refractive index ofapproximately 1.5 is used. As a resin for sealing in phosphor particles,methyl phenyl silicone or a silicone resin different in composition,such as dimethyl silicone, may be used. Alternatively, as long asappropriate for the intended use, another resin may be used. Forexample, when the optical semiconductor device 1A has a low luminanceand thus the sealing resin will not be degraded by blue light, a resinsuch as an epoxy resin, a hybrid resin of an epoxy resin and a siliconeresin, or a urethane resin may be used as the sealing resin.

The fluorescent layer 4 is formed by mixing phosphor particles in asilicone resin. The phosphor particles convert blue light intolong-wavelength light. The fluorescent layer 4 has a thickness of 15 μm,for example. As the silicone resin, methyl phenyl silicone having arefractive index of approximately 1.5, which is also used for theadhesive layer 3, is used. However, the silicone resin used for thefluorescent layer 4 is not limited to this, but may be another resin.Meanwhile, as the phosphor, used is YAG:Ce, which is yttrium aluminatedoped with cerium as an activator and which has a particle diameter notmore than 10 μm. Alternatively, as the phosphor, (Sr, Ba)₂SiO₄, which isstrontium-barium silicate doped with europium as an activator,Ca_(p)(Si, Al)₁₂ or the like may be used according to need. Moreover,the mixed phosphor need not necessarily be made of a material having asingle composition, but may be made of a mixture of two materials: onefor wavelength conversion from blue light into green light; the otherfor wavelength conversion from blue light into red light.

The light-transmissive layer 5 is made of a transparent substrate madeof a material such as optical glass or quartz. The light-transmissivelayer 5 has a thickness of 200 μm, for example. The material of thelight-transmissive layer 5 is not limited to the transparent substrate,but may be another light-transmissive material. In other words, thelight-transmissive layer 5 needs only to be made of a light-transmissivesubstrate made of a light-transmissive inorganic material. However, inthe interest of light extraction efficiency of the optical semiconductordevice 1A, a substrate having as a low refractive index as possiblewithin a range from 1.0 to 2.0 should preferably be used as thelight-transmissive substrate. This reduces a difference in refractiveindex between the fluorescent layer 4 and the air, and thus can improvethe light extraction efficiency of the optical semiconductor device 1A.

The reflective layer 6 is made of a metal such as Ag or Al, and has athickness of 0.3 μm, for example. The reflective layer 6 is provided onthe entire region (first region) of the lower surface (in FIG. 1) of thesecond cladding layer 2 b in the light-emitting layer 2. Specifically,an Ni/Au contact electrode (not shown) is formed by depositing metalssuch as Ni and Au in a thickness of 0.1 μm/0.1 μm on the lower surfaceof the second cladding layer 2 b, and the reflective layer 6 having athickness of 0.3 μm is then formed thereon.

The first electrode 7 a is formed by depositing metals such as Ni and Auin a thickness of 0.1 μm/0.1 μm, and thus has a thickness of 0.2 μm. Thefirst electrode 7 a, which is formed in a circle having a diameter of100 μm, is provided on an exposed region (second region) of the lowersurface (in FIG. 1) of the first cladding layer 2 a in thelight-emitting layer 2 (see FIG. 2).

Each second electrode 7 b is also formed by depositing metals such as Niand Au in a thickness of 0.1 μm/0.1 μm, and thus has a thickness of 0.2μm. The second electrodes 7 b, each of which is formed in a circlehaving a diameter of 100 μm, are provided on the lower surface (inFIG. 1) of the reflective layer 6 with a 200 μm pitch (see FIG. 2).

The first metal post 8 a is formed of a metal such as Cu to have acolumnar shape. The first metal post 8 a has a height of approximately103 μm and a diameter of 100 μm. A current flows between the first metalpost 8 a and the first electrode 7 a. Note that the shapes of the firstelectrode 7 a and the first metal post 8 a may be changed according toneed.

Each second metal post 8 b is formed of a metal such as Cu to have acolumnar shape. The second metal post 8 b has a height of approximately100 μm and a diameter of 100 μm. A current flows between the secondmetal post 8 b and the corresponding second electrode 7 b. Like thesecond electrodes 7 b, the second metal posts 8 b are provided with a200 μm pitch (see FIG. 2). Note that the shapes of the second electrodes7 b and the second metal posts 8 b may be changed according to need.

The insulating layer 9 is made of SiO₂, and functions as a passivationfilm (protective film). The insulating layer 9 has a thickness of 0.3μm. The insulating layer 9 entirely covers the light-emitting layer 2including the ends thereof, and thus prevents a current from flowingfrom the outside into the light-emitting layer 2 excluding the first andsecond electrodes 7 a and 7 b. This can prevent defects such as shortcircuit attributable to the phenomenon that mounting solder creeps up.

The sealing layer 10 is formed of a thermosetting resin, and has athickness of approximately 100 μm like the metal posts 8 a and 8 b. Thesealing layer 10 is provided on the entire surface of the insulatinglayer 9 so as to seal in the first and second metal posts 8 a and 8 bwhile leaving one ends thereof exposed. Accordingly, the circumferentialsurface of each of the first and second metal posts 8 a and 8 b iscompletely covered with the sealing layer 10.

Note that, though provided so as to entirely cover the light-emittinglayer 2 including the ends thereof, the insulating layer 9 need notnecessarily be provided in this manner. Alternatively, not theinsulating layer 9 but the sealing layer 10 may be provided so as toentirely cover the light-emitting layer 2 including the ends thereof. Inthis case as well, a current is prevented from flowing from the outsideinto the light-emitting layer 2 excluding the first and secondelectrodes 7 a and 7 b. Accordingly, defects such as short circuitattributable to the phenomenon that mounting solder creeps up can beprevented.

Each of the first and second metal layers 11 a and 11 b is formed bydepositing metals such as Ni and Au in a thickness of 0.1 μm/0.1 μm. Thefirst metal layer 11 a is provided on the end, that is, the exposedportion, of the first metal post 8 a. Each second metal layer 11 b isprovided on the end, that is, the exposed portion, of the correspondingsecond metal post 8 b. Note that the first metal layer 11 a has the samecircular planar shape as the first electrode 7 a, and each second metallayer 11 b has the same circular planar shape as each second electrode 7b (see FIG. 2).

In the optical semiconductor device 1A as described above, when voltagesare applied to the first and second metal posts 8 a and 8 b, theresultant potential is supplied to the first cladding layer 2 a throughthe first metal post 8 a, and the resultant potential is supplied to thesecond cladding layer 2 b through the second metal posts 8 b. As aresult, light beams are emitted from the active layer 2 c held betweenthe first and second cladding layers 2 a and 2 b. Some of the emittedlight beams are transmitted through the light-transmissive layer 5, andemitted from the surface of the light-transmissive layer 5 withoutreflection. Some of the emitted light beams are reflected by thereflective layer 6, then transmitted through the light-transmissivelayer 5, and emitted from the surface of the light-transmissive layer 5.Others are incident on the phosphor particles included in thefluorescent layer 4, so that the phosphor particles are excited to emitlight beams. Some of the light beams emitted from the phosphor particlesare also transmitted through the light-transmissive layer 5, and emittedfrom the surface of the light-transmissive layer 5. Others are alsoreflected by the reflective layer 6, then transmitted through thelight-transmissive layer 5, and emitted from the surface of thelight-transmissive layer 5. In this way, the blue light beams emittedfrom the light-emitting layer 2 and the (yellow, or red and green) lightbeams emitted from the phosphor particles that are excited by the bluelight beams are mixed into white light, which is emitted from thesurface of the light-transmissive layer 5.

With the above-described structure, the optical semiconductor device 1Ais simplified in configuration, and miniaturized to have a plane area assmall as that of the light-emitting layer 2. In addition, the structureeliminates the need for molding, a mounting step and a connecting stepin manufacturing the optical semiconductor device 1A. Accordingly, theoptical semiconductor device 1A can be manufactured by using normalsemiconductor manufacturing equipment, and thus can be manufactured atreduced cost. Moreover, in the structure, the fluorescent layer 4 forwavelength conversion from blue light into long-wavelength light isformed on the light-emitting layer 2, and the reflective layer 6 isformed under the lower surface of the light-emitting layer 2 (in FIG.1). Accordingly, by causing the light-emitting layer 2 to emit bluelight only upward, white light can be emitted toward the top surface (inFIG. 1) of the optical semiconductor device 1A. In addition, thelight-transmissive layer 5 formed on the fluorescent layer 4 reduces therefractive index difference between the fluorescent layer 4 and the air,which allows the optical semiconductor device 1A to have improved lightextraction efficiency. Furthermore, the above-mentioned structure allowsthe optical semiconductor device 1A, which has a plane area as small asthat of the light-emitting layer 2, to be reliably mounted on a glassepoxy board, which is a typical wiring board. This is because the metalposts 8 a and 8 b reduce the linear expansion coefficient differencebetween the light-emitting layer 2 and the glass epoxy board.

As described above, according to the first embodiment of the presentinvention, the optical semiconductor device 1A having theabove-described structure is obtained as follows. Firstly, thefluorescent layer 4 is provided on the light-emitting layer 2, and alight-transmissive inorganic material is then deposited on thefluorescent layer 4 so as to serve as the light-transmissive layer 5.Thereafter, the first metal post 8 a is provided on the first electrode7 a of the light-emitting layer 2, and the second metal posts 8 b areprovided on the respective second electrodes 7 b of the light-emittinglayer 2. Then, the sealing layer 10 is provided on the light-emittinglayer 2 so as to seal in the first and second metal posts 8 a and 8 b.In this optical semiconductor device 1A, the light-transmissive layer 5is made of an inorganic material, and thus prevented from being degradedby light (blue light, in particular) emitted from the light-emittinglayer 2. Accordingly, the life reduction of the optical semiconductordevice 1A is suppressed. In addition, having a simplified structure, theoptical semiconductor device 1A may be manufactured at reduced cost.Accordingly, cost reduction of the optical semiconductor device 1A canbe achieved. Moreover, having a simplified structure and a plane area assmall as that of the light-emitting layer 2, the optical semiconductordevice 1A can be miniaturized approximately to the size of a typicaloptical semiconductor element.

(Second Embodiment)

With reference to FIG. 3, a second embodiment of the present inventionwill be described. In the second embodiment of the present invention,only differences from the first embodiment will be described. Note that,in the second embodiment, the same parts as those in the firstembodiment are denoted by the same reference numerals, and thedescription thereof is omitted.

As shown in FIG. 3, in an optical semiconductor device 1B according tothe second embodiment of the present invention, the first metal layer 11a and the second metal layers 11 b are solder bumps. In other words, ahemispherical solder bump having a diameter of 100 μm, is formed on eachof the first and second metal posts 8 a and 8 b. The solder bump is madeof a solder material used for surface mounting, such as Sn-3.0Ag-0.5Cu,Sn-0.8Cu and Sn-3.5Ag.

As described above, the second embodiment of the present invention canprovide the same effects as the first embodiment. Moreover, since thefirst metal layer 11 a and the second metal layers 11 b are formed ofsolder bumps, the optical semiconductor device 1B has a larger gap froma wiring board on which the optical semiconductor device 1B is mountedthan the optical semiconductor device 1A according to the firstembodiment. Accordingly, when the optical semiconductor device 1B ismounted on the wiring board, a stress attributable to the linearexpansion coefficient difference between the optical semiconductordevice 1B and the wiring board can be further reduced.

(Third Embodiment)

With reference to FIGS. 4 and 5, a third embodiment of the presentinvention will be described. In the third embodiment of the presentinvention, only differences from the first embodiment will be described.Note that, in the third embodiment, the same parts as those in the firstembodiment are denoted by the same reference numerals, and thedescription thereof is omitted.

As shown in FIGS. 4 and 5, in an optical semiconductor device 1Caccording to the third embodiment of the present invention, the firstelectrode 7 a is formed as a square 100 μm on a side on the lowersurface (in FIG. 4) of the first cladding layer 2 a. Meanwhile, on thelower surface (in FIG. 4) of the second cladding layer 2 b, the secondelectrode 7 b is formed as a square 500 μm on a side with a square 150μm on a side cut out. Specifically, the cutout portion corresponds tothe corner region of the first cladding layer 2 a. The first metal post8 a is a rectangular column having the same planar shape as the firstelectrode 7 a, while the second metal post 8 b is a rectangular columnhaving the same planar shape as the second electrode 7 b. Moreover, thefirst metal layer 11 a has the same planar shape as the first electrode7 a, the second metal layer 11 b has the same planar shape as the secondelectrode 7 b (see FIG. 5).

As described above, the third embodiment of the present invention canprovide the same effects as the first embodiment. Moreover, in theoptical semiconductor device 1C according to the third embodiment, theplane area of each of the first and second electrodes 7 a and 7 b isincreased, and thus the plane area of each of the first and second metalposts 8 a and 8 b is increased, compared to the optical semiconductordevice 1A according to the first embodiment. This expands heatdissipation paths for allowing heat generated during light emission toescape from the optical semiconductor device 1C, and thus reducesthermal resistance thereof. This allows the optical semiconductor device1C to generate a reduced amount of heat during the passage of a current,and to have a greatly reduced transient thermal resistance.

(Fourth Embodiment)

With reference to FIG. 6, a fourth embodiment of the present inventionwill be described. In the fourth embodiment of the present invention,only differences from the first embodiment will be described. Note that,in the fourth embodiment, the same parts as those in the firstembodiment are denoted by the same reference numerals, and thedescription thereof is omitted.

As shown in FIG. 6, an optical semiconductor device 1D in according tothe fourth embodiment of the present invention does not include theadhesive layer 3, and the fluorescent layer 4 is formed directly on thefirst main surface M1 of the light-emitting layer 2. The fluorescentlayer 4 has a thickness of 10 μm, and is formed on the first mainsurface M1 of the light-emitting layer 2 by a method such as sputteringor chemical vapor deposition (CVD). The light-transmissive layer 5 isformed on the fluorescent layer 4 by, for example, applying a liquidglass onto the fluorescent layer 4 by spin coating, and then hardeningthe liquid glass.

As described above, the fourth embodiment of the present invention canprovide the same effects as the first embodiment. Moreover, theabove-described structure can eliminate, from the manufacturing process,a step of blending phosphor particles with a silicone resin and a stepof bonding the fluorescent layer 4 onto the light-emitting layer 2, bothof which are needed in the manufacturing process of the opticalsemiconductor device 1A according to the first embodiment. Thus, thefourth embodiment can reduce the manufacturing process time and thecost.

(Fifth Embodiment)

With reference to FIG. 7, a fifth embodiment of the present inventionwill be described. In the fifth embodiment of the present invention,only differences from the first embodiment will be described. Note that,in the fifth embodiment, the same parts as those in the first embodimentare denoted by the same reference numerals, and the description thereofis omitted.

As shown in FIG. 7, an optical semiconductor device 1E according to thefifth embodiment of the present invention does not include the adhesivelayer 3, and the fluorescent layer 4 is formed directly on the firstmain surface M1 of the light-emitting layer 2. In this embodiment, thefluorescent layer 4 consists of two layers, namely, fluorescent layers 4a and 4 b respectively made of materials mutually different incomposition. Specifically, on the light-emitting layer 2, sequentiallyformed are the fluorescent layer 4 a for wavelength conversion from bluelight into green light, and the fluorescent layer 4 b for wavelengthconversion from blue light into red light. Each of the fluorescentlayers 4 a and 4 b has a thickness of 10 μm, and is formed on the firstmain surface M1 of the light-emitting layer 2 by a method such assputtering or chemical vapor deposition (CVD). The light-transmissivelayer 5 is formed on the fluorescent layer 4 by, for example, applying aliquid glass onto the fluorescent layer 4 b by spin coating, and thenhardening the liquid glass.

As described above, the fifth embodiment of the present invention canprovide the same effects as the first embodiment. Moreover, theabove-described structure can eliminate, from the manufacturing process,a step of blending phosphor particles with a silicone resin and a stepof bonding the fluorescent layer 4 onto the light-emitting layer 2, bothof which are needed in the manufacturing process of the opticalsemiconductor device 1A according to the first embodiment. Thus, thefifth embodiment can reduce the manufacturing process time and the cost.

(Sixth Embodiment)

With reference to FIGS. 8 to 19, a sixth embodiment of the presentinvention will be described. In the sixth embodiment of the presentinvention, a method for manufacturing the optical semiconductor device1A according to the first embodiment will be described. Note that thismanufacturing method can be used as a method for manufacturing theoptical semiconductor device 1C according to the third embodiment. Inthe sixth embodiment, the same parts as those in the first embodimentare denoted by the same reference numerals, and the description thereofis omitted.

Firstly, as shown in FIG. 8, InGaN light-emitting layers 12 that emitblue light are formed on a substrate 11, which is a sapphire waferhaving a diameter of two inches and a thickness of 200 μm. Specifically,a light-emitting layer is formed by epitaxial growth, and then separatedinto the light-emitting layers 12 by reactive ion etching (RIE). In thisway, the light-emitting layer 2 of the optical semiconductor device 1Ais formed. The light-emitting layer 2 is formed by forming the firstcladding layer 2 a on a square region 550 μm on a side, and then formingthe second cladding layer 2 b on a region, not including a corner region(a square 150 μm on a side), of the lower surface of the first claddinglayer 2 a with the active layer 2 c interposed therebetween (see FIGS. 1and 2).

Then, as shown in FIG. 9, multi-layer films 13 are formed on therespective light-emitting layers 12 on the substrate 11. Specifically,Ni/Au films (not shown) having a thickness of 0.1 μm/0.1 μm are firstlyformed on the entire surfaces of the light-emitting layers 12 bysputtering so as to serve as contact layers of the light-emitting layers12, respectively. Then, metal films (not shown) made of Ag or Al andhaving a thickness of 0.3 μm are formed on the respective Ni/Au films bysputtering. In this way, the reflective layer 6 of the opticalsemiconductor device 1A is formed. Thereafter, Ni/Au films (not shown)having a thickness of 0.1 μm/0.1 μm, which are to be formed intoelectrodes, are respectively formed on electrode portions of thelight-emitting layers 12. Then, SiO₂ passivation films (not shown)having a thickness of 0.3 μm are formed by sputtering on regions otherthan the electrode portions of the light-emitting layers 12. In thisway, the first electrode 7 a, the second electrodes 7 b and theinsulating layer 9 of the optical semiconductor device 1A are formed. Asdescribed above, the multi-layer films 13 are formed on the respectivelight-emitting layers 12 on the substrate 11.

Then, as shown in FIG. 10, a seed layer 14, which is a conductive filmserving as a power feeding layer for plating, is formed on the entiresurface of the substrate 11 by a physical deposition method such asvapor deposition or sputtering. As this seed layer 14, a multi-layerfilm such as a Ti/Cu film is used. When the Ti/Cu film is employed, theTi layer, which is formed to increase adhesion strength between the seedlayer 14 and a resist or pads, needs only to have a thickness as smallas 0.1 μm. Meanwhile, the Cu layer, which mainly contributes to powerfeeding, should preferably have a thickness not smaller than 0.2 μm.

Thereafter, as shown in FIG. 11, a resist layer 15 serving as asacrifice layer is formed on the entire surface of the substrate 11. Theresist layer 15 has openings at electrode pad portions which are to beformed into the first and second electrodes 7 a and 7 b. As the resist,a photosensitive liquid resist or a dry film resist may be used.Specifically, the resist layer 15 is formed on the entire surface of thesubstrate 11 by forming a resist layer on the substrate 11, and thenforming the openings in this resist layer by exposure and developmentusing a light shield mask. After development, the resist may be bakeddepending on its material.

Then, as shown in FIG. 12, plated layers 16 are formed by electroplatingin the respective openings of the resist layer 15. In this way, themetal posts 8 a and 8 b of the optical semiconductor device 1A areformed. In electroplating, the substrate 11, which is a wafer, isimmersed in a plating liquid consisting of materials such as coppersulphate and sulphuric acid. Under this condition, current is caused toflow through the substrate 11 by connecting the seed layer 14 to thenegative terminal of a direct-current power source, and connecting a Cuplate, serving as an anode, to the positive terminal of thedirect-current power source, and thus Cu plating starts. Here, the Cuplate is placed so as to face the to-be-plated surface of the substrate11. Before the thickness of the plated layer, which increases with time,reaches that of the resist layer 15, the current is stopped, and thusthe plating is completed.

After the plating, as shown in FIG. 13, the resist layer 15 is peeledoff the substrate 11, and then the seed layer 14 is etch removed by acidcleaning. Thereby, the light-emitting layers 12, the multi-layer films13 and the plated layers 16 are exposed.

Then, as shown in FIG. 14, a thermosetting resin layer 17 to serve as asealing layer is formed on the entire surface of the substrate 11.Specifically, a thermosetting resin is applied by spin coating aroundthe plated layers 16 in a thickness to allow the plated layers 16embedded therein. Thereafter, the resultant substrate 11 is put in anoven and heated, and thus the thermosetting resin layer 17 is hardened.The resin can be hardened by being heated at 150° C. for two hours, forexample.

After that, as shown in FIG. 15, the surface of the thermosetting resinlayer 17 is ground off so that ends of the respective plated layers 16can be exposed. In this way, the sealing layer 10 of the opticalsemiconductor device 1A is formed. The thermosetting resin layer 17 isgrounded by rotational grinding using a rotational grinding wheel, andthus the surface thereof can be planarized after being ground. Afterground, the substrate 11 may be dried according to need. Note that, inthe previous step, it is difficult to apply a thermosetting resin by amethod such as spin coating with only the ends of the plated layers 16exposed (It requires much time and cost). Accordingly, this grindingstep is necessary for exposing the ends of the plated layers 16 afterthe spin coating step.

Then, as shown in FIG. 16, the light-emitting layers 12 are lifted offthe substrate 11 by irradiating the interface between the substrate 11and the light-emitting layers 12 with laser beams. Thereby, alight-emitting substrate 12A formed of the light-emitting layers 12, themulti-layer films 13, the plated layers 16 and the thermosetting resinlayer 17 is separated off the substrate 11. The light-emitting layers 12are lifted off the substrate 11 by causing an Nd:YAG third harmoniclaser to irradiate the interface therebetween with laser beams having awavelength of 355 nm through the substrate 11. Note that the liftoffstep is optional, and thus may be omitted.

Then, as shown in FIG. 17, the surface, at which the light-emittinglayers 12 are exposed, of the light-emitting substrate 12A formed bythis liftoff step is bonded onto a fluorescent layer 19 that is providedon a light-transmissive substrate 18, such as an optical glass waferwith an adhesive layer 20 interposed therebetween. This fluorescentsubstrate on which the light-emitting substrate 12A is bonded is formedin another step. Specifically, a silicone resin layer mixed withphosphor particles is formed as the fluorescent layer 19 on thelight-transmissive substrate 18 made of a light-transmissive inorganicmaterial, and another silicone resin layer is formed as the adhesivelayer 20 on the silicone resin layer. In this way, thelight-transmissive layer 5, the fluorescent layer 4 and the adhesivelayer 3 of the optical semiconductor device 1A are formed.

Here, the phosphor particles and the silicone resin are uniformly mixedusing a rotary and revolutionary mixer, and then applied onto thelight-transmissive substrate 18 by spin coating. The resultantlight-transmissive substrate 18 is put in an oven, and the siliconeresin is hardened therein. The silicone resin used here can be hardenedby being heated at 150° C. for an hour, for example. In order to formthe fluorescent layer 4 in a uniform thickness, after applied onto thelight-transmissive substrate 18, the silicone resin is hardened withspacers formed thereon, and with jigs having anti-sticking surfacescoated with fluorine attached thereon. Thereby, the curvature of thesurface of the silicone resin film attributable to surface tension canbe suppressed, and thus the silicone resin film having a uniformthickness can be formed.

The light-emitting layers 12 are bonded onto the fluorescent layer 19,which is a silicone resin layer mixed with phosphor particles, asfollows. Firstly, a silicone resin is applied onto the fluorescent layer19 (or the light-emitting layers 12) by spraying. After that, thelight-emitting substrate 12A appropriately positioned and stacked on thelight-transmissive substrate 18. The light-emitting substrate 12A andthe light-transmissive substrate 18 thus stacked are put into an oven,and bonded together by hardening the silicone resin therein. Thesilicone resin can be hardened by being heated at 150° C. for an hour,for example.

Then, as shown in FIG. 18, Ni/Au layers 21 are formed by electrolessplating on the respective plated layers 16 to serve as Cu electrodes. Inthis way, the metal layers 11 a and 11 b of the optical semiconductordevice 1A are formed. In Ni electroless plating, the wafer is firstlydegreased by, for example, being treated with a slightly alkalinedegreasing liquid for three minutes, and is then washed with runningwater for one minute. Thereafter, the wafer is acid cleaned, and thenimmersed in a nickel-phosphorus plating liquid at liquid temperatureadjusted to 70° C. Thereafter, the wafer is washed with water, and thusthe Ni layers are formed. In addition, in Au electroless plating, thewafer is immersed in an electroless gold plating liquid at liquidtemperature adjusted to 70° C. Thereafter, the wafer is washed withwater and then dried. In this way, the surfaces of the respective Cuelectrodes are plated.

Lastly, as shown in FIG. 19, the resultant stack is diced into themultiple optical semiconductor devices 1A using a dicer. In this way,the optical semiconductor device 1A according to the first embodiment isobtained. Note that approximately the same steps as above are employedin the manufacturing process of the optical semiconductor device 1Caccording to the third embodiment. By changing the size and shape of theopenings in the resist layer 15, the optical semiconductor device 1Caccording to the third embodiment can be obtained.

As described above, according to the sixth embodiment of the presentinvention, the optical semiconductor device 1A according to the firstembodiment can be manufactured. Thus, the sixth embodiment can providethe same effects as the first embodiment. In addition, by changing thesize and shape of the openings in the resist layer 15, the opticalsemiconductor device 1C according to the third embodiment can bemanufactured. Thus, the sixth embodiment can provide the same effects asthe third embodiment. Moreover, the sixth embodiment allows a largenumber of optical semiconductor devices 1A or 1C to be manufacturedthrough a single manufacturing process, and thus allows mass productionof the optical semiconductor devices 1A or 1C. Therefore, the sixthembodiment can suppress the costs of the optical semiconductor devices1A and 1C.

(Seventh Embodiment)

With reference to FIGS. 20 to 23, a seventh embodiment of the presentinvention will be described. In the seventh embodiment of the presentinvention, a method for manufacturing the optical semiconductor device1B according to the second embodiment will be described. Note that, inthe seventh embodiment, the same parts as those in the second embodimentare denoted by the same reference numerals, and the description thereofis omitted.

The manufacturing process according to the seventh embodiment of thepresent invention has the same steps as those in the sixth embodimentfrom the step of forming the light-emitting layers 12 shown in FIG. 8 tothe bonding step shown in FIG. 17.

After the bonding step, as shown in FIG. 20, contact layers 31 such asNi/Au layers are formed on by electroless plating on the respectiveplated layers 16 to serve as Cu electrodes. In Ni electroless platingand Au electroless plating, the same processes are performed as those inthe step of forming the Ni/Au layers 21 according to the sixthembodiment.

Then, as shown in FIG. 21, a solder paste 32 made of Sn-3.0Ag-0.5Cu isapplied onto the contact layers 31 by printing. Note that the method forapplying the solder paste 32 is not limited to printing.

Then, as shown in FIG. 22, the light-transmissive substrate 18, which isa wafer, is passed through a reflow furnace. As a result, the solder isremelted and a flux residue is cleaned off. Thereby, solder bumps 33 areformed on the respective plated layers 16 to serve as Cu electrodes. Inthis way, the metal layers 11 a and 11 b of the optical semiconductordevice 1B are formed.

Lastly, as shown in FIG. 23, the resultant stack is diced into themultiple optical semiconductor devices 1B using a dicer. In this way,the optical semiconductor device 1B according to the second embodimentis obtained.

As described above, according to the seventh embodiment of the presentinvention, the optical semiconductor device 1B according to the secondembodiment can be manufactured. Thus, the seventh embodiment can providethe same effects as the second embodiment. Moreover, the seventhembodiment allows a large number of optical semiconductor devices 1B tobe manufactured through a single manufacturing process, and thus allowsmass production of the optical semiconductor devices 1B. Therefore, theseventh embodiment can suppress the costs of the optical semiconductordevices 1B.

(Eighth Embodiment)

With reference to FIGS. 24 to 27, an eighth embodiment of the presentinvention will be described. In the eighth embodiment of the presentinvention, a method for manufacturing the optical semiconductor device1D according to the fourth embodiment will be described. Note that thismanufacturing method can be used as a method for manufacturing theoptical semiconductor device 1E according to the fifth embodiment. Inthe eighth embodiment, the same parts as those in the fourth embodimentare denoted by the same reference numerals, and the description thereofis omitted.

The manufacturing process according to the eighth embodiment of thepresent invention has the same steps as those in the sixth embodimentfrom the step of forming the light-emitting layers 12 shown in FIG. 8 tothe liftoff step shown in FIG. 16.

After the liftoff step, as shown in FIG. 24, a fluorescent layer 41 isformed on the surface, at which the light-emitting layers 12 areexposed, of the light-emitting substrate 12A, by using a sputteringapparatus. In this way, the fluorescent layer 4 of the opticalsemiconductor device 1D is formed. Alternatively, the fluorescent layer41 may be formed to have a multi-layer structure by performingsputtering multiple times. In this case, the fluorescent layer 4 of theoptical semiconductor device 1E according to the fifth embodiment can beformed. Note that the fluorescent layer 41 may alternatively be formedusing a CVD apparatus.

Then, as shown in FIG. 25, a liquid glass is applied onto thefluorescent layer 41 by spin coating, and then hardened. Thereby, alight-transmissive layer 42 is formed on the fluorescent layer 41. Inthis way, the light-transmissive layer 5 of the optical semiconductordevice 1D is formed. Besides spin coating, the method for applying theliquid glass may be spraying, and does not particularly limited. Theglass layer can be hardened by being heated at 200° C. for an hour, forexample. Besides a liquid glass, any material may be used for thelight-transmissive layer 42 according to need.

Then, as shown in FIG. 26, Ni/Au layers 43 are formed on by electrolessplating on the respective plated layers 16 to serve as Cu electrodes. Inthis way, the metal layers 11 a and 11 b of the optical semiconductordevice 1D are formed. In Ni electroless plating and Au electrolessplating, the same processes are performed as those in the step offorming the Ni/Au layers 21 according to the sixth embodiment.

Lastly, as shown in FIG. 27, the resultant stack is diced into themultiple optical semiconductor devices 1D using a dicer. In this way,the optical semiconductor device 1D according to the fourth embodimentis obtained. Note that approximately the same steps as above areemployed in the manufacturing process of the optical semiconductordevice 1E according to the fifth embodiment. By performing sputteringmultiple times in the step of forming the fluorescent layer 41 to causethe fluorescent layer 41 to have a multi-layer structure, the opticalsemiconductor device 1E according to the fifth embodiment can beobtained.

As described above, according to the eighth embodiment of the presentinvention, the optical semiconductor device 1D according to the fourthembodiment can be manufactured. Thus, the eighth embodiment can providethe same effects as the fourth embodiment. In addition, by causing thefluorescent layer 41 to have a multi-layer structure, the opticalsemiconductor device 1E according to the fifth embodiment can bemanufactured. Thus, the eighth embodiment can provide the same effectsas the fifth embodiment. Moreover, the sixth embodiment allows a largenumber of optical semiconductor devices 1D or 1E to be manufacturedthrough a single manufacturing process, and thus allows mass productionof the optical semiconductor devices 1D or 1E. Therefore, the eighthembodiment can suppress the costs of the optical semiconductor devices1D and 1E.

(Other Embodiments)

Note that the present invention is not limited to the foregoingembodiments, and may be variously changed without departing from thegist of the present invention. For example, some of the components shownin the foregoing embodiments may be omitted. In addition, the componentsin different ones of the embodiments may be used in combinationaccording to need. Moreover, specific values used in the foregoingembodiments are only examples, and thus the present invention is notlimited to these.

What is claimed is:
 1. An optical semiconductor device to be mounted ona wiring board, comprising: a first resin layer; a second resin layerstacked with the first resin layer, the second resin layer covering anactive layer without interposing a growth substrate therebetween, asurface of the active layer facing toward the first resin layer, a sidesurface of the active layer being enclosed by the second resin layer,the second resin layer enclosing conductive portions being used to causea current for exciting the active layer to flow through the activelayer, and the conductive portions having ends which are to be connectedto the wiring board, and a light transmitting material stacked on thefirst resin layer.
 2. The optical semiconductor device according toclaim 1, wherein the first resin layer includes a fluorescent material,and the second resin layer does not include the fluorescent material. 3.The optical semiconductor device according to claim 1, wherein theoptical semiconductor device has a surface where only the first resinlayer is exposed to outside of the optical semiconductor device.
 4. Theoptical semiconductor device according to claim 1, comprising: the firstresin layer attached to the active layer on a first side of first resinlayer; and the light transmitting material attached to the first resinlayer on a second side of the first resin layer opposite to the firstside.